Ram Yamsaengsung

Modeling the transport phenomena and structural changes during deep fat frying Part I: model development

A fundamental 2-D model was developed to predict the heat and mass transfer that occur during the frying and cooling process of tortilla chips. Semi-empirical correlations were included to account for structural changes, such as shrinkage and expansion due to puffing. All water present in the tortilla chip was considered bound and led to shrinkage when removed. The parameters that were studied included water saturation, Sw, oil saturation, So, temperature, T, and pressure, P. Liquid flow results from convective flow due to the gradient in total gas pressure and capillary flow due to the gradient of capillary force. Gas movement results from convective flow due to the total gas pressure gradient and Knudsen diffusion due to the concentration gradient. The only transport phenomenon during cooling is oil absorption, which is assumed to be a function of the capillary pressure. � 2002 Elsevier Science Ltd. All rights reserved.

Modeling the transport phenomena and structural changes during deep fat frying Part II: model solution & validation

Abstract A fundamental two-dimensional model to predict the heat and mass transfer that occur during the frying and cooling process of tortilla chips was solved using finite element technique. The assembly of elements method with each element being four-noded quadrilateral elements was used to obtain a two-dimensional distribution. The Gauss–Legendre method was used for the numerical integration of each of the integrals. The system of non-linear equations (including contributions from all elements) was solved using FORTRAN Power Station 4.0. A good agreement between experimental and predicted data was obtained. The parameters that were studied included water saturation, oil saturation, temperature during frying and cooling. Change in structure (shrinkage and expansion) was also verified and agreed well with the experimental data. Sensitivity analysis showed that the higher frying temperature the faster drying rate and a faster increase in the temperature and pressure of the product. More oil was absorbed at a lower frying temperature. The thicker the product the lesser the oil content. Oil absorption appeared to seize once the temperature of the product begins to increase and a crust begins to form. The cooling temperature had the most influence on oil absorption. The cooling temperature that was nearest to the temperature of the fried product led to the least amount of oil absorption.

Superheated Steam Vacuum Drying of Rubberwood

The effect of superheated steam vacuum drying (SSVD) on the drying time and mechanical properties of rubberwood was studied. Rubberwood boards with dimensions of 1000 mm × 76.2 mm × 25.4 mm were dried at 86.7–89.3 kPa vacuum pressure (14.6–12.0 kPa absolute) and temperatures of 60, 70, and 80°C. Superheated steam at 110°C was injected intermittently to relieve stress buildup in wood and eliminate cracking. The prong test was used to evaluate the initial acceptability of the dried wood and the mechanical properties of wood were measured. From this study, the total drying time was reduced from 168 h to less than 20 h (MC reduction from 0.80 to 0.06 db). In addition, compared to the reference values shown in the parentheses, the shear parallel-to-grain, the compression parallel-to-grain, the compression perpendicular-to-grain, the modulus of rupture (MOR), the modulus of elasticity (MOE), and the hardness for the optimum drying temperature of 70°C were 28.87 (11.0) MPa, 59.09 (32.0) MPa, 21.09 (5.0) MPa, 101.97 (66.0) MPa, 9838.5 (9240.0) MPa, and 6475 (4350) N, respectively. Thus, the vacuum-dried wood showed a 32% increase in hardness, a 12% increase in compression parallel-to-grain, and an 88% increase in shear parallel-to-grain.

Pilot-scale steam explosion for xylose production from oil palm empty fruit bunches and the use of xylose for ethanol production.

Pilot-scale steam explosion equipments were designed and constructed, to experimentally solubilize xylose from oil palm empty fruit bunches (OPEFB) and also to enhance an enzyme accessibility of the residual cellulose pulp. The OPEFB was chemically pretreated prior to steam explosion at saturated steam (SS) and superheated steam (SHS) conditions. The acid pretreated OPEFB gave the highest xylose recovery of 87.58 ± 0.21 g/kg dried OPEFB in the liquid fraction after explosion at SHS condition. These conditions also gave the residual cellulose pulp with high enzymatic accessibility of 73.54 ± 0.41%, which is approximately threefold that of untreated OPEFB. This study has shown that the acid pretreatment prior to SHS explosion is an effective method to enhance both xylose extraction and enzyme accessibility of the exploded OPEFB. Moreover, the xylose solution obtained in this manner could directly be fermented by Candida shehatae TISTR 5843 giving high ethanol yield of 0.30 ± 0.08 g/g xylose.

Hybrid Drying of Rubberwood Using Superheated Steam and Hot Air in a Pilot-Scale

A pilot-scale rubberwood dryer was constructed and injected with superheated steam and hot air to study the effect of the hybrid system on the drying rate and mechanical properties of the wood. A total of 300 pieces of rubberwood boards, each with dimensions of 1000 mm long × 76.2 mm wide × 25.4 mm thick, were stacked in 1.0 m × 1.0 m × 1.7 m (1.7 m3) pallet. The stack was impinged with alternating cycles of superheated steam and hot air. The time required for conventional drying was 168 hours, but the drying time for the hybrid system was only 64 hours, resulting in a 62% reduction. After being dried, the rubberwood boards were mechanically tested for static bending, compression strength, hardness, and shear strengths. From the mechanical tests, the hybrid drying system using superheated steam and hot air had no significant effect on the mean shear strength parallel-to-grain; however; the mean compression strength parallel-to-grain was reduced by 24.2% and the mean MOR by 21.4%. Nonetheless, the mean MOE was increased by 30.4% and the mean of hardness by 16.4%.

Precipitated Silica Derived from Palm Oil Mill Fly Ash: Kinetics and Characterization

The silica extraction from palm oil mill fly ash (POMFA) using sodium hydroxide as one of viable processes for obtaining silica from agricultural waste was investigated. The effects of extraction time and temperature were closely examined to study the kinetics of the process. The fixed variables used in the present work were mass of POMFA 468.2 gram; the POMFA mass to NaOH volume ratio 0.2341 g/cm3; the concentration of NaOH 1.4 N and the stirring speed of 1065 RPM. The levels of temperature employed were 348 K, 358 K, 368 K and 378 K for different time durations up to 60 min. The mechanical fragmentation process was applied to obtain precipitated silica from the extracted silica. The precipitation conditions were: stirring speed of 1160 RPM, pH of 8.75, temperature of 303 K and precipitation time of 100 min. The shrinking core model (SCM) with intra-particle diffusion controlled mechanism and the Jander equation can satisfactorily represent the extraction process. The activation energy for silica extraction was 58.20 kJ/mol for the SCM with intra-particle diffusion and 62.22 kJ/mol for the Jander equation respectively. The precipitated silica agglomerate obtained at the time of 100 min has the median-weighed volume particle size distribution of 114.07 μm. The chemical composition and physical characteristic of precipitated silica which were analyzed with LPSA, XRF, XRD, FTIR and SEM are similar to the precipitated silica from the references.